Four aspeets of advances in inborn errors of metabolism (IEM) are analysed: 1) concerning the general comprehension of the pathogenesis, genic localization and genetic heterogeneity; 2) clinicai aspeets, with description of new variants of known IEM or new IEM; 3) laboratory diagnostic tests presently used in our country: dosage of some genetic markers (arylsulfatases, hexosaminidases, beta-glicosidase; beta-galactosidase and sphingomyelinase), newborn populational screening (for hyperphenylalaninemia, and hypothyroidism), heterozygote detection (for Tay-Sachs disease) and also some prenatal diagnosis; 4) therapeutic aspects presenting substitutive treatment, special diets, plasma pheresis and leucopheresis. The first results of 4 cases of mucopolysacharidosis treated with the last technic are presented.